1. Field of the Invention
The present invention relates to a method for detecting a moving object from an image photographed by a video camera or the like, and apparatus for the same.
2. Relevant Art
In public places where a large and unspecified number of persons enter and leave (e.g., banks, stores, etc.) and/or where dangers are generated by unwanted intrusions (e.g., electric power plants, power transmission facilities, etc.), video cameras are currently installed at predetermined positions, and the generation of abnormal situations is checked by means of viewing the image taken from this video camera. However, with respect to this image viewing model, normally, a person (in charge) must continually watch the monitor screen, and thus this method is rather undesirable from the viewpoint of labor saving. In addition, another method for detecting the generation of abnormal situations can be considered in which the image taken from the video camera is recorded on videotape and viewed afterwards by the person-in-charge using high-speed play. In this case, it is possible to reduce the actual working time of the person in charge; however, this method poses disadvantages in that it is not possible for the person-in-charge to detect an abnormal situation immediately following the generation of this abnormal situation.
In consideration of the aforementioned, a method is proposed in which the image of a moving object, such as an unexpected intruder or the like, is automatically recognized from among the images taken by the video camera. Models of this nature include, for example, a method for detecting a moving object by means of obtaining the deviation whereby the difference between images of each frame is minimized; and a method for detecting a moving object by means of conducting a Fourier transformation of the image at each frame and then detecting the moving object from the ratio of the aforementioned Fourier transformation from the preceding and subsequent frames. However, in these methods, disadvantages exist in that due to the necessity of conducting complex computations at a high precision over an extremely short time period, a system for conducting high-speed processing is necessary, thereby leading to high costs. In addition, other disadvantages exist in that when viewing outdoor scenes in which the background presents a number of complex movements, e.g., the swaying of trees or the like, due to the existence of a large number of objects other than that intended for detection, it is extremely difficult to distinguish the object to be detected from the movements of the aforementioned.
With regard to these drawbacks, a moving object detecting apparatus for detecting the image of a moving object by means of image processing using a comparatively simple computation without performing high-speed processing, has been proposed. For example, the image processing apparatus disclosed in Otsuki, et al., (U.S. Pat. No. 5,212,547: May 1993) averages a plurality of past images to form a standard image, calculates the difference between the color data of each pixel of this standard image (hereinafter referred to as "dot data") and the dot data of the present image corresponding to this aforementioned dot data, and then finally detects this calculated difference as the image of a moving object.
According to this type of apparatus, the detected moving object is statistically recognized by means of forming the aforementioned standard image, and stochastic inference or judgment is then possible with respect to this statistical recognition. In addition, the objective detection of fuzziness is also possible. Furthermore, it is also possible to determine membership function from an objective standpoint, and minimize the influence of noise contained in the image at each instant. This type of apparatus can, moreover, be constructed at a comparatively low cost, and is superior in that precise detection of abnormal phenomena is possible.
However, according to the image processing apparatus disclosed in Otsuki, et al., (U.S. Pat. No. 5,212,547: May 1993), at the time of forming a standard image, in the case where a moving object appears over the majority of a plurality of past images to be averaged, a standard image containing the image of this moving object is inevitably formed. When attempting to detect only the moving object from the image of the present time point using this standard image, the image of only the moving object at the present time point, as well as the image of the moving object contained in the standard image, as an afterimage of the aforementioned moving object, are detected.
In addition, in the formation of the above standard image, when the number of samples of past images, from which an average is to be taken, is small, the aforementioned afterimage appearing in the detection result is particularly remarkable. For example, the appearance of an afterimage in the detection result is maximized in an apparatus for detecting an image of a moving object by means of comparing an image at a time point from a predetermined period of the past and an image at the present time point, without using the aforementioned standard image.
In this manner, when the aforementioned afterimage appears in the detection result, it becomes difficult to distinguish the actual size, shape, etc. of the original moving object to be detected. In addition, in cases where the afterimage is extremely remarkable, it becomes difficult to even specify the moving object itself.